Outside of his specialty, McKay is best known for his collaborative work with a group of Israeli mathematicians such as Dror Bar-Natan and Gil Kalai, together with Maya Bar-Hillel, who rebutted a Bible code theory which maintained that the Hebrew text of the Bible enciphered predictive details of future historical events. The paper in question had been accepted for publication in a scientific peer-reviewed journal in 1994.[7][8][9] Their rebuttal, together with a paper written by an anonymous mathematician, argued that the patterns in the Bible that supposedly indicate some hidden message from a divine source or have predictive power can be just as easily found in other works, such as War and Peace.[10] The discredited theory was taken up by Michael Drosnin.[11][12] Drosnin said he was convinced of this theory when one of its exponents stated that the Torah predicted the Iraqi wars. He expressed his certainty publicly that such coded messages could not be found in any other work than the Bible, and, in an interview with Newsweek, he challenged:

"When my critics find a message about the assassination of a prime minister encrypted in Moby Dick, I'll believe them."

This debunking disproof of a theory that the bible encrypts secret messages containing future world history achieved international fame for McKay outside of his specific field of combinatorics.[14][15][16]

McKay was involved in the uncovering of the original source of the Azzam Pasha quotation. The original source, an October 11, 1947 article in the Egyptian newspaper Akhbar al-Yom, was first referenced in an article by David Barnett and Efraim Karsh in the Fall 2011 issue of in Middle East Quarterly without reference to McKay.[17]Tom Segev responded in an op-ed in Haaretz that McKay had in fact been the original source of the material and had uploaded it to Wikipedia.[18] McKay had notified the Wikipedia talk page of having found the original interview from which the quote was taken and later provided it to Barnett. According to Karsh, McKay was offered a co-author credit in the Middle East Quarterly article but he declined on the grounds of having a low opinion of the publication.[19]